Coaxial switches and power dividers



May 16, 1961 G. J. WHEELER COAXIAL SWITCHES AND POWER DIVIDERS R m 5 M WW J m M s A m 6 w A TTORNE Y COAXIAL SWITCHES AND POWER DIVIDERS Gershon J. Wheeler, Los Altos, Calif., assignor to Raytheon Company, a corporation of Delaware Filed Nov. 24, 1958, Ser. No. 775,916

13 Claims. (Cl. 333-4) This invention relates to electromagnetic wave transmission systems and more particularly to a combined switch, power divider and signal mixer employing structures which may be formed from coaxial transmission line components.

Since coaxial transmission line structures can generally be readily constructed for use over a broad band of frequencies extending from and including the higher frequencies at which lumped-element structures are feasible to construct, to and including a substantial portion of the lower end of the frequency range over which electromagnetic wave waveguide structures of practicable physical dimensions can be conveniently constructed, the provision of the coaxial transmission line structures of the present invention represents a valuable and substantial contribution to the art. in other words, the useful frequency range over which coaxial transmission line structures can, as a feasible and practicable matter, be used, substantially overlaps (or extends into) both the lumped-element range and the waveguide range, in addition to including the intermediate frequency range which is too high for practicable lumped-element structures and too low for practicable waveguide structures.

Various forms of microwave switches and directional couplers have been heretofore proposed, but in general these switches and couplers have had the disadvantage of being cumbersome to operate, difficult to design, requiring special matching provisions to reduce discontinuity eifects and likewise such switches are capable of use only in a narrow band of frequencies, i.e., require narrow band components.

One form of prior art device for coupling an electromagnetic wave from one coaxial conductor to another consisted of two coaxial conductors with the respective outer conductors contiguous and having holes out on the common area so that coupling takes place through these holes. Such devices, while functioning as a coupler, are generally diflicult to design and incapable of functioning as a switch. Other prior art coaxial devices utilized involve ring or rat-race arrangements and the like and are similarly limited in their operation.

In accordance with a preferred embodiment of the invention, a four-terminal network or system comprises a pair of parallel coaxial lines coupled together by two half wave coaxial stubs having parallel axes spaced apart a quarter Wavelength and at right angles to the parallel coaxial lines. A quarter wavelength distance at the frequency of operation from parallel coaxial lines, i.e., half way from each coaxial line, a quarter wavelength branch is connected between the half wavelength coaxial branches to form two square rings or loops a quarter wavelength on a side wherein one branch is common to both rings and each ring contains a remote branch not common to any other ring. At each apex of the quarter wavelength branch and the half wavelength branch there is provided an adjustable shorting stub having an operative length greater than one-half wavelength. The shorting elements in the shorting stubs are each spaced away Patented May 16, 1961 from the quarter wavelength branch an equal distance and are mechanically interconnected whereby they may be adjusted in unison from an odd number of quarter wavelengths to an even number of quarter wavelengths.

The invention may also be described as a four-terminal network comprising two parallel coaxial lines coupled together by an odd number of quarter wavelength coaxial branches spaced a quarter wavelength apart to form a chain of at least two square rings or loops a quarter wavelength on a side. The chain contains an even number of loops or meshes. Two shorting stubs, as described hereinbefore, are operatively located at the junctions of the cen ter branch and axis of symmetry. In both of the above branch and axis of symmetry. In both of the above cases, which are full equivalents, each quarter wavelength section of the four-terminal networks has an admittance of unity normalized to the main coaxial lines.

A principal object of the invention is, therefore, to provide structures composed principally of coaxial line elements which will have, particularly in and adjacent to the frequency range intermediate to the feasible lumped-element and waveguide frequency ranges, the the characteristics of a switch, power divider, a hybrid junction, signal mixer and directional coupler.

Another object of the invention is to provide a simple mechanical device for switching electromagnetic waves from one electromagnetic wave circuit to another.

Another object of the invention is to provide a means for coupling together two transmission lines having parallel central axes.

A still further object of the invention is to provide a compact coaxial or strip line switch that is simple, smaller and lighter than waveguide switches and that additionally may function as a power divider, mixer for two microwave signals and an attenuator.

These and other objects and features of the invention, together with their incident advantages, will be more readily understood and appreciated from the following detailed description of the preferred embodiment thereof selected for purposes of illustration and shown in the accompanying drawing, in which:

Fig. 1 is a perspective view with parts broken away showing the invention as a coaxial switch and power divider; and

Fig. 2 is an illustration of the invention in slightly different form from that shown in Fig. 1.

In the following description, the expressions line, branch and stub are used for the sake of simplicity. These terms should be interpreted as including coaxial lines, hollow waveguides, strip lines, and the like.

Referring now to Fig. 1, which shows a four-terminal coaxial network incorporating the present invention, two parallel main coaxial lines 1-2 are coupled together by three branches 9lil-11 each a quarter wavelength long and having parallel axes spaced apart a quarter Wavelength, as shown. The inner conductors 13-14 of each main coaxial line 1-2 are connected to the inner conductors 1516l7 of each quarter wavelength branch 9-10-11 to form a four-terminal network. The inner conductors of the main coaxial lines and branches may be centrally supported with respect to their outer conductors by any suitable means, such as supporting insulators or the like.

The network includes, as shown in Fig. 1 and Fig. 2, seven line or branch sections 36, 47, 58, and 3-4, 45, 67, 78, the references 3 to 8 designating the apices of the network meshes. The references 3, 5, 6 and 8 also designate four terminals of the network that may be located in two separate lines that might be straight as shown in Fig. 1, or U-shaped as shown in Fig. 2. By way of example, a source of electromagnetic energy (not shown) may be connected to terminal 3 and terminals 5, 6 and 8 may be utilized as output terminals to any conventional device.

The inner conductor 18 of an upstanding shorting stub 19 is connected to the network at the apex 4 of the inner conductor 13 of the main coaxial line 1 and the inner conductor 16 of branch 10. A shorting element 21 longitudinally movable a distance at least greater than one-half the wavelength of the desired frequency of operation and spaced one quarter wavelength away from apex 4 electrically connects the outer conductor 22 and inner conductor 18 of the shorting stub 19. A shorting stub 23, identical to shorting stub 19, is connected at apex 7 of the inner conductor 14 of the main coaxial line 2 and the inner conductor 16 of branch and a shorting element 24, identical to shorting element 21, is mechanically connected to shorting element 21, whereby both shorting elements may be adjusted in unison from apices 47 from an odd number of quarter wavelengths to an even number of quarter wavelengths at the frequency of operation. An analysis of a fourterminal symmetrical network substantially identical with the network as hereinbefore described, with the exception of the shorting stubs, is contained in an article entitled A Method of Analysis of Symmetrical FourPort Networks by John Reed and Gershon J. Wheeler; I.R.E. Transactions on Microwave Theory and Techniques, vol. MTT-4, No. 4, October 1956. All pertinent parts of this article are, accordingly, incorporated in the present application and made a part thereof, by reference. Although the type of four-terminal network analyzed in the above referenced article can function only as a coupler, the invention as described hereinabove is a substantial improvement thereover and may function as a compact coaxial switch, power divider, attenuator, mixer, or directional coupler. If each quarter wavelength branch of the network has an admittance of unity normalized to the main lines and the shorting stubs also have unit admittance, any one of the branches of the network is matched for all positions of the shorting stubs, and no power supplied to terminal 3 will reach terminal 5. Similarly, no power supplied to terminal 6 will reach terminal 8. However, if the length of the shorting stubs 1923 is adjusted to an odd number of quarter wavelengths, all of the power from terminal 3, for example, will be supplied to terminal 6. Similarly, all of the power supplied to terminal 5 will be supplied to terminal 8. On the other hand, if the length of the shorting stubs 1923 is adjusted to have a length equal to an even number of quarter wavelengths, all of the power supplied to terminal 3 will be connected to terminal 8, and all of the power supplied to terminal 5 will be connected to terminal 6. For other values of the length of the shorting stubs between an odd number of quarter wavelengths and an odd number of half wavelengths, power supplied to terminal 3, for example, will divide between terminal 8 and terminal 6. Similarly, power supplied to terminal 5 will also divide between terminal 8 and terminal 6.

In view of the preceding discussion, it may now be obvious that the invention may be used as a switch by adjusting the length of the shorting stubs through a distance equal to a quarter wavelength. For example, if the length of the shorting stubs is adjusted to an odd number of quarter wavelengths, power supplied to terminal 3 will be connected to terminal 6. If the length of the shorting stubs is adjusted a quarter wavelength in either direction, the power from terminal 3 previously supplied to terminal 6 will now be switched from terminal 6 to terminal 8 and during switching the energy source will see a good impedance match. Obviously, power can be divided, for example, in any desired proportion between terminals 8 and 6 by adjusting the shorting stubs to an appropriate length.

The network may be utilized as an attenuator, for example, by supplying power to terminal 3 and terminating terminal 8 in a suitable load (not shown) to absorb unwanted power. Adjustment of the shorting stubs to the proper length, as discussed hereinbefore, results in a division of power between terminals 6 and 8 when power is supplied initially to terminal 3. This same principle of cross transfer holds true if, for example, power is supplied to terminal 5, 6 or 3.

The invention may be used to switch two signals simultaneously. If two signals are fed separately to terminals 3 and 5, the shorting stubs, when adjusted to the proper length, will switch the signal at terminal 3 to terminal 8 and the signal at terminal 5 to terminal 6 or, alternately, switch the signal at terminal 3 to terminal 6 and the signal at terminal 5 to terminal 8.

Inasmuch as the invention functions as a power divider, as pointed out hereinbefore, it may be apparent that the device is equally useful to mix two signals. Consider a signal supplied to terminal 6 and a separate signal supplied to terminal 8. Upon adjustment of the shorting stub to a length intermediate a quarter wavelength and a half wavelength, a portion of the signal at terminal 6 and 8 will be supplied to each of the terminals 3 and 5.

Fig. 2 shows the invention in slightly diiferent form wherein the main coaxial lines 12 are now oppositely disposed and U shaped instead of parallel as shown in Pig. 1. With the above exception, the structure and operation thereof as shown in Fig. 2 is identical with that shown in Fig. 1. If the end portions of lines 12 of Fig. l are visualized as being bent outwardly at right angles, the similarity between Fig. l and Fig. 2 will immediately become apparent.

While the present invention has been described in its preferred embodiment, it is realized that modifications may be made, and it is desired that it be understood that no limitations on the invention are intended other than may be imposed by the scope of the appended claims.

What is claimed is:

1. In an electromagnetic wave transmission system having a plurality of terminals the combination comprising: a plurality of meshes each having four branches, said meshes being connected together to form a chain so that adjacent ones of said meshes have one branch in common, the outer meshes of said chain having a remote branch that is not common to other meshes of said chain, said terminals being. located at the ends of selected ones of said branches, the number of said meshes being such that the system has a line of symmetry substantially coincident with one of the common branches; two shorting stubs each connected to one end of said common branch coincident with said line of symmetry; and means to vary the eifective length of said shorting stubs in unison.

2. In an electromagnetic wage transmission system having a plurality of terminals the combination comprising: a plurality of meshes each having four branches effectively a quarter wavelength long at the frequency of operation, said meshes being connected together to form a chain so that adjacent ones of said meshes have one branch in common, the outer meshes of said chain having a remote branch that is not common to other meshes of said chain, said terminals being located at selected ends of said remote branches, the number of said meshes being such that the system has a line of symmetry substantially coincident with one of the common branches; two shorting stubs at least a quarter wavelength long at the frequency of operation each connected to one end of said common branch coincident with said line of symmetry; and means to vary the eifective length of said shorting stubs in unison.

3. In an electromagnetic wave transmission system having four terminals the combination comprising: a plurality of meshes each having four branches effectively a quarter wavelength long at the frequency of operation, said meshes being connected together to form a chain so that adjacent ones of said meshes have one branch in common, the outer meshes of said chain having a remote branch that is not common to other meshes of said chain, two of said four terminals being located at the ends of each of said remote branches, the number of said meshes being such that the system has a line of symmetry substantially coincident with one of the common branches; two adjustable shorting stubs at least a quarter wavelength long at the frequency of operation each connected to one end of said common branch coincident with said line of symmetry, the effective length of each said shorting stub being substantially equal at all times; and means to vary the effective length of said shorting stubs in unison.

4. In an electromagnetic wave transmission system having four terminals the combination comprising: a plurality of meshes each having four branches effectively a quarter wave-length long at the frequency of operation, said meshes being connected together to form a chain so that adjacent ones of said meshes have one branch in common, the outer meshes of said chain having a remote branch that is not common to other meshes of said chain, two of said four terminals being located at the ends of each of said remote branches, the number of said meshes being such that the system has a line of symmetry substantially coincident with one of the common branches; two adjustable shorting stubs having a predetermined length each connected to one end of said common branch coincident with said line of symmetry, the eifective length of each said shorting stub being substantially equal at all times; and means to vary the eflective length of said shorting stubs in unison from an odd number of quarter wavelengths to an even number of quarter wavelengths at the frequency of operation.

5. A switch for coupling electromagnetic energy from a main transmission line to two secondary transmission lines comprising: a plurality of meshes each having four branches having an admittance of unity normalized to the said main transmission line, said meshes being connected together to form a chain so that adjacent ones of said meshes have one branch in common, the outer meshes of said chain having a remote branch that is not common to other meshes of said chain, said main transmission line and one of said secondary transmission lines being connected to the ends of one of said remote branches, said other secondary transmission line being connected to the end of the other remote branch diagonally opposite from said main transmission line, the number of said meshes being such that the system has a line of symmetry substantially coincident with one of the common branches; two shorting stubs having a predetermined length each connected to one end of said common branch coincident with said line of symmetry; and means to vary the effective length of said shorting stubs in unison through about a quarter wavelength at the frequency of operation.

6. A switch for coupling electromagnetic energy from a main transmission line to two secondary transmission lines comprising: a plurality of meshes each having four branches having an admittance of unity normalized to the said main transmission line, said meshes being connected together to form a chain so that adjacent ones of said meshes have one branch in common, the outer meshes of said chain having a remote branch that is not common to other meshes of said chain, said main transmission line and one of said secondary transmission lines being connected to the ends of one of said remote branches, said other secondary transmission line being connected to the end of the other remote branch diagonally opposite from said main transmission line, the number of said meshes being such that the system has a line of symmetry substantially coincident with one of the common branches; two variable shorting stubs having a predetermined length each connected to one end of said common branch coincident with said line of symmetry, the effective length of each said shorting stub being substantially equal at all times; and means to vary the efiective length of said shorting stubs in unison up to a quarter wavelength.

7. A switch for coupling electromagnetic energy from a main transmission line to two secondary transmission lines comprising: a plurality of meshes each having four coaxial branches each effectively a quarter wavelength long at the frequency of operation, said meshes being connected together to form a chain so that adjacent ones of said meshes have one coaxial branch in common, the outer meshes of said chain having a remote coaxial branch that is not common to other meshes of said chain, said main transmission line and one of said secondary transmission lines being connected to the ends of one of said remote coaxial branches, said other secondary transmission line being connected to the end of the other remote coaxial branch diagonally opposite from said main transmission line, the number of said meshes being such that the system has a line of symmetry substantially coincident with one of the common branches; two variable shorting stubs substantially an even number of quarter wavelengths long at the frequency of operation each connected to one end of said common branch coincident with said'line of symmetry, the eifective length of each said shorting stub being substantially equal at all times; and means for varying the effective length of said shorting stubs in unison from an odd number of quarter wavelengths to an even number of quarter wavelengths at the frequency of operation.

8. A directional coupler device comprising: a plurality of n1 loops, where n is equal to at least three, each of said loops consisting of four lines each effectively a quarter wavelength long at the frequency of operation, said lines being connected together to form loops having four apices; connections for connecting adjacent ones of said loops together so that one of the aforesaid lines and two of the apices of the adjacent loops are common thereto, to form a chain of loops, said chain having a pair of outer loops each having a pair of apices that are not common with other loops of said chain; an input terminal connected to one of said pair of the apices of one of said outer loops; a first output terminal connected to the other apex of said last mentioned pair of apices; second and third output terminals each connected to the apices of the other of said pair of apices; a first shorting stub separated from respectively said input terminal and said third output terminal by at least one of said lines, said first shorting stub being separated from said first and second output terminals by at least two of said lines; a second shorting stub separated from respectively each of said first and second output terminals by at least one of said lines, said second shorting stub being separated from said input terminal and said third output terminal by at least two of said lines, said first and second shorting stubs being substantially an even number of wavelengths long at the frequency of operation; and means for simultaneously varying the effective length of said shorting stubs while maintaining the effective lengths of said shorting stubs equal one with another from an odd number of quarter wavelengths to an even number of quarter wavelengths.

9. A directional coupler device comprising: an even number of loops, each of said loops consisting of four coaxial lines a quarter wavelength long at the frequency of operation, said lines being connected together to form substantially square loops having four apices; connections for connecting adjacent ones of said loops together so that one of the aforesaid lines and two of the apices of the adjacent loops are common thereto, to form a chain of loops, said chain having a pair of outer loops each having a pair of apices that are not common with other loops of said chain, an input terminal connected to one of said pair of the apices of one of said outer loops; a first output terminal connected to the other apex of said last mentioned pair of apices; second and third output terminals each connected to the apices of the other of said pair of apices; a firstshorting stub separated from respectively said input terminal and said third output terminal by at least one ofsaid lines, said first shorting stub being separated from said first and second output terminals by at least two of said lines; a second shorting stub separated from respectively each of said first and second output terminals by at least one of said lines, said second shorting stub being separated from said input terminal and said third output terminal by at least two of said lines, said first and second shorting stubs being substantially an even number of wavelengths long at the frequency of operation; and means for simultaneously varying the effective length of said shorting stubs from an odd number of quarter wavelengths to an even number of quarter wavelengths while maintaining the etfective lengths of said shorting stubs equal one with another.

10. In an electromagnetic wave transmission system for coupling electromagnetic energy from a main transmission line to two secondary transmission lines the combination comprising: a plurality of meshes each having four branches having an admittance of unity normalized to the said main transmission line, said meshes being connected together to form a chain so that adjacent ones of said meshes have one branch in common, the outer meshes of said chain having a remote branch that is not common to other meshes of said chain, said main transmission line and one of said secondary transmission lines being connected to the ends of one of said remote branches, said other secondary transmission line being connected to the end of the other remote branch diago- 8 nally opposite from said main transmission line, the number of said meshes being such that the system has a line of symmetry substantially coincident with one of the common branches; and two shorting stubs of predetermined length each connected to one end of said common branch coincident with said line of symmetry.

11. The combination as defined in claim 10 wherein the predetermined length of said shorting stubs is substantially equal to an odd number of quarter wavelengths at the operating frequency.

12. The combination as defined in claim 10 wherein the predetermined length of said shorting stubs is substantially equal to an even number of quarter wavelengths at the operating frequency.

13. The combination as defined in claim 10 wherein the predetermined length of said shorting stubs in intermediate an even number of quarter wavelengths and an odd number of quarter wavelengths at the operating frequency.

References Cited in the file of this patent UNITED STATES PATENTS 2,590,373 Brudley Mar. 25, 1952 2,605,356 Ragan July 29, 1952 2,685,065 Zaleski July 27, 1954 OTHER REFERENCES Mia UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,984,797 4 May 16 1961 Gershon Wheeler It is hereby certified that error appears in the above numbered paten'b requiring correction and that the said Letters Patent should read as corrected below,

Column 2, lines 13 and 14, strike out "In both of the 1 above branch and axis of symmetry".

Signed and sealed this 21st day of November 1961.

(SEAL?) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents USCOMM-DC 

